so returning the same type makes the patching code above easier

... that we need to rewrite differently.

While running tests, I came across a strange test failure where
each(List,Closure) is delegating to each(Iterator,Closure) and results
in a cast failure. Obviously, it shuold have resolved to
each(Object,Closure) instead.

This got me thinking about how Groovy resolves overloaded methods, which
is non-trivial as a dynamic language.

So in this change I'm changing the code so that Groovy doesn't have to
resolve overloaded versions correctly.

The correct signature, which you can check in DefaultGroovyMethods, is
to return the 'self' type

…if only once, rather than merely returning the list element.

The suspected cause of the problem is that DGMPatcher is not touching
everything it needs to touch, when Groovy runtime is already warm and
cached lots of MetaMethod objects.

This test, having a name that is alphabetically before
CpsTransformerTest, runs before that and populates the cache, exposing
the defect in DGMPatcher.

Run the test like this:

  mvn clean test -Dtest=AaaMakeGroovyBusy,CpsTransformerTest

…at elements overriding Object.equals.

... and cast wider net to traverse a bigger graph

…4' into DGMPatcher-Groovy-2-JENKINS-34064

Conflicts:
	src/main/java/com/cloudbees/groovy/cps/impl/DGMPatcher.java

…4064

Reverting cloudbees#38 in this branch.

…nued

Conflicts:
	src/test/groovy/com/cloudbees/groovy/cps/CpsTransformerTest.groovy